In a combustion chamber of an internal combustion engine, a mixture of air and fuel is compressed and then is ignited in that state. It is known that the compression ratio when compressing the air-fuel mixture can affect the output of the internal combustion engine and the amount of fuel consumption. By raising the compression ratio, the output torque can be made larger and the thermal efficiency can be improved. In this regard, if making the compression ratio too high, it is known that knocking and other abnormal combustion will occur. In the prior art, an internal combustion engine changing the compression ratio during its operating period has been known.
Japanese Patent Publication No. 2005-214088A discloses a variable compression ratio engine able to make a reciprocating operating member advance and retract so as to change the position where a piston reaches top dead center. This variable compression ratio engine uses an actuator mechanism to change the compression ratio. The actual mechanism is provided with a ball screw, a rotation transmission system transmitting rotation of a motor to the ball screw, and a clutch interposed in the rotation transmission system. This publication discloses to employ a reverse input restricting type clutch which transmits rotation from an input member to which drive force of the motor is input to a nut, but which blocks transmission of rotation from the nut to the input member.